Compact solar-powered air conditioning systems

Abstract

A design of a compact solar air conditioning system especially suited for tropical climates includes an air-cooled single-effect absorption machine driven by an array of high performance flat-plate collectors along with a thermal storage tank. The absorption machine uses lithium-bromide as a refrigerant and a water-based absorption fluid. The operation of the compact solar air conditioning system is determined by an optimal control strategy.

We claim:  
     
       1. A compact solar-powered air conditioning system operable without the use of a cooling tower comprising: 
       a plurality of solar collectors positioned to collect energy and configured to heat a fluid along a path that passes through the solar collectors;  
       a storage tank coupled with the solar collectors and configured to store the heated fluid after passing through the solar collectors; and  
       an absorption machine operationally coupled with the storage tank and configured to draw the heated fluid from the storage tank to drive a refrigeration loop, wherein the absorption machine includes:  
       a desorber that receives the heated fluid and causes a refrigerant to change from a liquid state to a gaseous state using energy from the heated fluid;  
       a condenser in communication with the desorber to receive the refrigerant in the gaseous state therefrom and configured to cause the refrigerant to return to a liquid state;  
       an evaporator in communication with the condenser to receive the refrigerant in the liquid state therefrom and to return the refrigerant to a gaseous state, wherein the change from the liquid state to the gaseous state is able to absorb energy from an external cooling loop;  
       an absorber in communication with the evaporator to receive the refrigerant in the gaseous state therefrom and configured to circulate an absorbent solution in the presence of the refrigerant, whereby the absorber releases heat of dilution and heat of condensation, and wherein the heat of dilution and the heat of condensation are exhausted by passing ambient air over the absorber, and  
       a housing that encloses the desorber, the condenser, the evaporator and the absorber, and wherein the housing defines a first air inlet and a first exhaust configured to permit the passage of ambient air through the housing and over the absorber.  
     
     
       2. The compact solar-powered air conditioning system of  claim 1 , wherein the plurality of solar collectors are connected in series and wherein the fluid that passes through the solar collectors comprises water. 
     
     
       3. The compact solar-powered air conditioning system of  claim 1 , wherein the storage tank comprises a stratified storage tank operable to draw the heated fluid to drive the refrigeration loop from a layer having a highest temperature. 
     
     
       4. The compact solar-powered air conditioning system of  claim 1 , further comprising a heater operationally positioned between the storage tank and the absorption machine and operable to further heat the heated fluid drawn from the storage tank when its temperature is insufficient to drive the refrigeration loop. 
     
     
       5. The compact solar-powered air conditioning system of  claim 1 , wherein the refrigerant comprises water. 
     
     
       6. The compact solar-powered air conditioning system of  claim 1 , wherein the absorbent comprises lithium-bromide. 
     
     
       7. The compact solar powered air conditioning system of  claim 1 , wherein the housing further comprises a second air inlet and a second exhaust configured to permit the passage of ambient air through the housing and over the condenser. 
     
     
       8. The compact solar powered air conditioning system of  claim 1 , wherein the absorption machine is configured to deliver a cooling load ranging from three to five tons. 
     
     
       9. A compact solar-powered air conditioning system operable without the use of a cooling tower comprising: 
       a plurality of solar collectors positioned to collect energy and configured to heat a fluid along a path that passes through the solar collectors;  
       a storage tank coupled with the solar collectors and configured to store the heated fluid after passing through the solar collectors;  
       a heater operationally positioned between the storage tank and the absorption machine and operable to further heat the heated fluid drawn from the storage tank when its temperature is insufficient to drive the refrigeration loop;  
       an absorption machine operationally coupled with the storage tank and configured to draw the heated fluid from the storage tank to drive a refrigeration loop, wherein the absorption machine includes:  
       a desorber that receives the heated fluid and causes a refrigerant to change from a liquid state to a gaseous state using energy from the heated fluid;  
       a condenser in communication with the desorber to receive the refrigerant in the gaseous state therefrom and configured to cause the refrigerant to return to a liquid state;  
       an evaporator in communication with the condenser to receive the refrigerant in the liquid state therefrom and to return the refrigerant to a gaseous state, wherein the change from the liquid state to the gaseous state is able to absorb energy from an external cooling loop; and  
       an absorber in communication with the evaporator to receive the refrigerant in the gaseous state therefrom and configured to circulate an absorbent solution in the presence of the refrigerant, whereby the absorber releases heat of dilution and heat of condensation, and wherein the heat of dilution and the heat of condensation are exhausted by passing ambient air over the-absorber; and  
       a housing that encloses the desorber, the condenser, the evaporator and the absorber, and wherein the housing defines a first air inlet and a first exhaust configured to permit the passage of ambient air through the housing and over the absorber, and a second air inlet and a second exhaust configured to permit the passage of ambient air through the housing and over the condenser; and wherein:  
       the absorption machine is configured to deliver a cooling load ranging from three to five tons;  
       the plurality of solar collectors are connected in series and the fluid that passes through the solar collectors comprises water;  
       the storage tank comprises a stratified storage tank operable to draw the heated fluid from a layer having a highest temperature;  
       the refrigerant comprises lithium-bromide; and  
       the absorbent comprises water.  
     
     
       10. A compact solar-powered air conditioning system comprising: 
       a plurality of solar collectors configured to circulate a fluid to collect energy;  
       a storage tank in communication with the plurality of solar collectors and configured to store the fluid after passing through the plurality of solar collectors; and  
       an absorption machine in communication with the storage tank and configured to draw the fluid from the storage tank to drive a cooling circuit, wherein the absorption machine includes:  
       an air-cooled condenser configured to extract heat by changing the state of a refrigerant from a vapor to a liquid; and  
       an air-cooled absorber coupled with the air-cooled condenser through an evaporator and configured to extract heat by absorbing a vapor refrigerant in a liquid absorbent; and  
       an enclosure housing the air-cooled absorber, and the air-cooled condenser and having a first air-flow path configured to pass ambient air across the air-cooled absorber and a second air-flow path configured to pass ambient air across the air-cooled condenser.  
     
     
       11. The compact solar-powered air conditioning system of  claim 10 , wherein the enclosure of the absorption machine further comprises a first duct defining the first air-flow path, and a second duct defining the second air-flow path, and wherein the first and second ducts maintain the first air-flow path separate from the second air-flow path. 
     
     
       12. The compact solar-powered air conditioning system of  claim 11 , wherein the enclosure of the absorption machine defines a first intake aperture for the first duct and a first exhaust aperture for the first duct, and a second intake aperture for the second duct and a second exhaust aperture for the second duct, and wherein the first intake aperture and the second intake aperture are separate, and the first exhaust aperture and the second exhaust aperture are separate. 
     
     
       13. The compact solar-powered air conditioning system of  claim 12 , wherein the enclosure defines at least four distinct surfaces including a top, front, rear and side surface, and wherein the side defines the first intake aperture and the front defines the first exhaust aperture, and wherein rear defines the second intake aperture and the top defines the second exhaust aperture. 
     
     
       14. The compact solar-powered air conditioning system of  claim 11 , wherein the absorption machine further comprises a first and a second fan, wherein the first fan is positioned to move ambient air through the first duct and the second fan is positioned to move ambient air through the second duct. 
     
     
       15. The compact solar powered air conditioning system of  claim 10 , wherein the storage tank further comprises a stratified storage tank so that the fluid drawn by the absorption machine is drawn from a layer within the storage tank having a temperature higher than other layers within the storage tank. 
     
     
       16. The compact solar-powered air conditioning system of  claim 10 , wherein the refrigerant comprises water and the absorbent comprises lithium-bromide. 
     
     
       17. The compact solar-powered air conditioning system of  claim 10 , wherein the air cooled condenser of the absorption machine comprises a plurality of parallel copper tubes that pass the refrigerant and a plurality of parallel aluminum fins each defining a plurality of passages for the copper tubes that pass therethrough so that heat from the refrigerant is conducted out of the copper tubes and through the aluminum fins. 
     
     
       18. A method of operating a solar-powered air conditioning system comprising the steps of: 
       drawing a fluid from a storage tank at a level having a lower temperature than other levels in the storage tank;  
       passing the fluid drawn from the storage tank at the level having the lower temperature through a plurality of solar collectors, wherein the fluid experiences an increase in temperature;  
       returning the fluid to the storage tank;  
       drawing the fluid from the storage tank at a level having a higher temperature than other levels of the storage tank;  
       passing the fluid drawn from the storage tank at the level having the higher temperature though an air-cooled absorption machine, wherein energy from the fluid drives a cooling loop configured to extract energy from a building, and  
       passing ambient air through a housing that encloses the absorption machine, wherein the air is drawn through an inlet in the housing, passes over at least a portion of the absorption machine, and is discharged through an outlet in the housing.  
     
     
       19. The method of  claim 18 , wherein the step of passing the fluid drawn from the storage tank at the level having the higher temperature through the air-cooled absorption machine further comprises: 
       liberating a water-based refrigerant from a liquid to a vapor state; and  
       absorbing the water-based refrigerant in a lithium-bromide absorbent.